hot engine 914 ULS start problems

by Nils Sparre in 912 / 914 Technical Questions 12 years ago

We have an 914 ULS engine in our Dynaero Mini Cruiser, The engine has only 7 hrs since new.It starts easily when cold , but is very difficult to restart when hot. Could it be that the heat of the engine will cause vopor lock in the carburator or manifold, after landing before engine being cooled down. We operate the turbo as recommended in Rotax manual. Someone has the same experiance , and how did you fix it.

Nils

Re: hot engine 914 ULS start problems

by Roger Lee » 12 years ago

Roger Lee

126 5.13k 4.56k

Hi Nils,

A couple of things may make it hard to start when hot. If the engine is in a nice tight cowl the fuel line will get hot after engine shut down as it sits and the heat under there builds up and this is especially true if the lines are not in the recommended fire sleeve. If you have metal lines the heat can cause a little vapor in the lines (depends on aircraft Mfg). If the idle is set too high and or you use the choke for a hot start it can cause a hard start. If the idle is set too low it can cause a hard start. If the carbs aren't synced. Most of the time these are the common factors for a hot start issue.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

Thank you said by: Nils Sparre

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Re: hot engine 914 ULS start problems

by Evan Gardiner » 12 years ago

Evan Gardiner

0 2 0

Hi Nils,

Regarding the vapour lock/hot start issue. I have an MCR ULC and it used to drive me nuts too. I suspect what is really happening here, is that after the engine is shut down, the heat under the cowl rises to the extent that the fuel boils in the carburettor and unloads some raw fuel into the intake manifold. The next engine start needs to deal with the dual problem of being choked with raw fuel in the intake manifold and a vapour lock in the fuel system.

The fix......and this works every time, is to turn the fuel cock off 2 or 3 minutes before shutting down the engine normally. With little fuel left in the carburettor there is no fuel to flood the intake manifold and the fuel lines between the fuel cock and the carburettors are empty of hot and vaporising fuel. Next engine start and the electric fuel pump recharges the whole fuel system with fresh fuel and the engine starts normally.

What about forgetting to turn the fuel on again before take off? Should be part of your pre take/off checks. But it is easy to time how long an engine takes to shut down at idle with the fuel cock turned off. So that then becomes your shut down routine, to wait until just before the engine starts to splutter before shutting it down. As long as the carburettors are mainly empty at shut down you will not be able to taxi very far without the fuel cock turned on, let alone be in position to start a take/off run.

Cheers,
Chunk

Thank you said by: Nils Sparre

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Re: hot engine 914 ULS start problems

by Nils Sparre » 12 years ago

Nils Sparre

1 1 0

Thanks it seems to work to turn the fuel off a few minutes before shutting down the engine

Nils

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Re: hot engine 914 ULS start problems

by James Butcher » 11 years ago

James Butcher

8 10 5

Chunk,

When you attempt the restart, do you use the choke just like when the engine is totally cold?

I tried doing as you suggested but still found it difficult to start the hot engine. I did not use the choke.

Thanks

Jim Butcher
Europa XS 914

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hot engine 914 ULS start problems

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